$small:1px;
$middle:2px;
$big:3px;
@mixin font-size($fontSize: 24px) {
    /* 兼容iphone5 */
    @media (device-height:568px) and (-webkit-min-device-pixel-ratio:2){
        font-size: $fontSize - $small;
    } 
    @media only screen and (max-device-width :480px){ 
        font-size: $fontSize - $small;
    } 
    @media only screen and (min-device-width :481px){ 
        font-size: $fontSize - $small;
    } 
    /*6*/ 
    @media (min-device-width : 375px) and (max-device-width : 667px) and (-webkit-min-device-pixel-ratio : 2){ 
        font-size: $fontSize;
    } 
    /*6+*/ 
    @media (min-device-width : 414px) and (max-device-width : 736px) and (-webkit-min-device-pixel-ratio : 3){
        font-size:$fontSize + $middle;
     } 
    /*魅族*/ 
    @media only screen and (min-device-width :1080px) and (-webkit-min-device-pixel-ratio : 2.5){ 
        font-size:$fontSize + $middle;
    } 
    /*mate7*/ 
    @media only screen and (min-device-width :1080px) and (-webkit-min-device-pixel-ratio : 3){
        font-size:$fontSize + $middle;
     } 
    /*4 4s*/ 
    @media only screen and (device-height :480px) and (-webkit-device-pixel-ratio:2){ 
        font-size:$fontSize - $small;
    } 
}